The present invention is concerned with power line carrier (PLC) information communication and, more specifically, with a method of, and apparatus for, utilizing magnetic coupling for exciting high-frequency PLC information onto and through system conductors.
It is often desirable to transmit information via one or more power line conductors, between locations adjacent to the conductors themselves. In order to carry out PLC communication, it is first necessary to effectively couple a PLC signal onto the involved system conductor. It has been found that the use of magnetic coupling often requires that several turns of wire be placed around a magnetic core, to maximize the coupling efficiency. However, the flow of current at the normal power line frequency (60 Hz in the United States) in the same coil generally causes the magnetic core to saturate, so that the PLC signal encounters a loss of coupling, production of non-linear intermodulation products, and the like deleterious consequences. A further impediment occurs if the conductor, into which the PLC signal current is to be injected, must be broken in order to insert a coupling coil; many safety regulations prohibit the breaking of the circuit conductors, especially when involving a neutral conductor, which is almost always required to be continuous. Further, it is often required that PLC signals be propagated around certain circuit elements, such as power-factor-correction capacitors, distribution transformers, and the like, which tend to act as undesirable impedances (or, even worse, as open circuits or short circuits) at the PLC frequency. Thus, it is highly desirable to provide a method and apparatus allowing the coupling of PLC information signals (at PLC frequencies at least two orders of magnitude higher than the power line frequency) to at least one distribution conductor, carrying the power frequency currents to system loads, while minimizing the impedance seen by those power frequency currents (and thus minimizing the power system losses) due to the PLC system components.